This study aims to investigate how nature of science activities affects pre-service science teachers’ critical thinking skills. The participants of this study are 62 pre service science teachers; 47 of which are girls and 15 are boys. Motivated Strategies for Learning Questionnaire (MSLQ), developed by Pintrich, Garcia, and McKeachie (1991), was used to assess students’ critical thinking skills for both pre-test and post-test. Real Fossils, Real Science, Tangram, Flojiston, The Tube, The Cans were activities that used in the present study to discuss nature of science. During the discussions, pre-service science teachers were encouraged about to dwell on the common misconceptions about the nature of science. A one- way within-subjects ANOVA test was conducted to compare pre-test and posttest results about students’ critical thinking skills. According to the results, there was a significant difference between pre-test and post-test. In other words, the results suggested that the nature of science activities is effective to improve pre-service science teachers’ critical thinking skills.